1. Field
The invention relates to sampling apparatus for removing a portion of the particulate matter from a stream of particulate material for sampling moisture and other physical characteristics and chemical composition. Samplers of this type are particularly useful in sampling streams of finely divided coal so that the moisture content, BTU content, sulfur content and the like may be determined. The sample removed from the mainstream must be representative of the material in the mainstream, that is, it is desirable that fine material not be lost during the collection of the sample.
2. Prior Art
A number of different devices have been utilized to divert particulate matter from a mainstream into a secondary stream so that the sample of the material in the mainstream may be taken. One widely utilized device for this purpose is the flop-gate.
A typical flop-gate construction comprises a main duct disposed vertically and having a square or rectangular cross-section. In one of the vertical walls a door is fitted which is pivoted along its lower edge. The width of the door is substantially the same as the width of the duct and the height of the door is greater than the width of the duct. Whenever it is desired to take a sample, the door is swung inward by pivoting about its lower edge so that it swings into the duct and substantially closes the duct to the flow of material as the material strikes the face of the door and discharges through the side opening in the duct into a sampling chute. The flop-gate is simple in construction. However, the device has disadvantages inasmuch as the door or gate cannot fit so tightly against the interior walls of the main duct to prevent a substantial amount of fine material from passing around the door. Also, since the gate closes against the stream of material it frequently does not close tight because it catches material between the upper edge of the door and the interior of the duct so that some material leaks into the sampler chute at times other than the sampling period.